Field of the Invention
The invention relates to an electromagnetic actuator as claimed herein and to a method for equalizing the pressure between an armature plate space and a control space of the electromagnetic actuator of this invention.
Background of the Invention
The current state of knowledge is as follows.
An electromagnetic actuator is known for example from DE 10 2007 013 525 A1.
Electromagnetic actuators are known, for example as solenoids or solenoid actuators, in which an armature is connected to a plunger moved by a magnetic force generated by the energization of the magnet coil in the direction of a pole core. The plunger thereby closes a control space, which comprises an actuating device. This actuating device, for example a switch or a valve device in a fluid power application, is actuated by the plunger, whereby, for example, an energization-dependent force is generated for pressure control by means of the magnet coil with which a sealing element, e.g. a ball of a valve, is pressed against the valve seat of the valve by the plunger, thereby adjusting or regulating the energization-dependent differential pressures. From EP 2 187 037 A1 a fuel metering unit is known for the intake-side delivery volume of a high pressure fuel pump of a fuel injection device for internal combustion engines, whereby this comprises a control valve actuated by an electromagnetic actuator. This actuator comprises a magnet coil, an armature arranged on a plunger that is guided in a bush and is so moved on energization of the solenoid by the magnetic force generated that the plunger protruding into a control space of a valve housing of the control valve actuates a piston-shaped valve element. In this case, the plunger is mounted on bearings arranged in the valve housing on the valve side in a cylinder, whereby the plunger is displaceable on the other side in a bearing bush at the opposite end of the valve housing, whereby the end of the plunger moves into a hollow space connected to this bearing bush.
During the operation of this known fuel metering unit, fuel is forcibly moved by the movement of the plunger inside the fuel metering unit. To avoid the function of the fuel metering unit being thereby hindered, it is proposed to form such a bearing bush with at least one axial groove to serve as a pressure compensation bore, which can be arranged both on its outside and on its inside. By means of such a bearing bush with axial grooves, pressure compensation bores can at least be partly avoided inside the valve housing and/or the armature.
However, this well-known measure of providing axial grooves in bearing bushes to serve as pressure compensation bores is not sufficient for reliable pressure compensation in unfavorable operating conditions of the electromagnetic actuator.
Thus, for example, pressure control valves for modern diesel common rail injection systems require very precise control of the injection pressure and need a high stability against both high pressure fluctuations as well as increasingly against increased pressures on the low pressure side.
In this case, pressure pulsation not only occurs in certain pressure ranges, but also often in unfavorable operating conditions, such as during a cold start of the engine at −25° C. These pressure pulsations in a high pressure accumulator (common rail) usually lead to vibrations in other attachments, for example tank lines, and are associated with a poorly running engine.
For completeness, reference is made to DE 10 2006 054 941 B3, which describes a solenoid having a cylindrical hollow and a magnetic body filled with a medium in which a stroke armature arrangement with an armature and a plunger is axially movable in the medium in the direction of actuation by a magnetic force. The plunger is anchored in an axial bore in the armature while the armature has pressure compensation bores to produce pressure compensation between the two end faces of the armature, which are arranged as close as possible in the region of the axial bores receiving the plunger. Thus, pressure compensation is achieved only in the swept volume of the armature. However, even this measure does not lead to a desired reduction of pressure pulsations in an electromagnetic actuator of the kind mentioned initially.
The invention has for its object the provision of an electromagnetic actuator of the type that reacts significantly more robustly to pressure pulsations.